1. Field of the Invention
The present invention relates to a polyamide resin composition which has excellent flowability and which can give a molded article with excellent mechanical strength, and heat resistance, and relates to a molded article composed of this composition.
2. Description of the Related Art
Aliphatic polyamides such as nylon 6 and nylon 66 have been used for engineering plastics in a variety of applications because of their excellent heat resistance, chemical resistance, rigidity, wear resistance, moldability, and so forth. In particular, when these aliphatic polyamides are used in electrical and electronic component applications, they need to have high flame retardance as set forth in UL-94, and, therefore, many different methods for making them flame resistant through the use of flame retardants have been proposed and put to practical use.
However, aliphatic polyamides can absorb water easily, which is a problem in that the resulting molded articles may cause dimensional change, blistering and reduction of physical properties. Furthermore, with electrical and electronics components which need to be made flame retardant, a mounting procedure called surface mounting technology (SMT) has rapidly gained acceptance because it allows components to be mounted in a higher density, makes the soldering process more efficient, and so forth. However, this approach cannot be applied to conventional aliphatic polyamides because of their low heat resistance. In particular, lead-free solder, which has a higher melting point than conventional lead solder, has recently become major due to environmental regulations, so the level of heat resistance required for SMT applications is even higher now. Also, SMT connectors have become thinner and lower in profile as the performance of cellular phones and personal computers has enhanced. In addition, injection molding, which allows numerous molded articles to be produced in one shot, has been employed recently in order to improve productivity, so there is now a need for a material that not only has good heat resistance, but also has high flowability and gives molded articles having excellent mechanical strength.
To this need, highly heat resistant semi-aromatic polyamides whose main component is a polyamide composed of terephthalic acid and an aliphatic alkylenediamine have come to be used in electrical and electronic component applications (see, for example, U.S. Pat. Nos. 5,258,439 and 5,256,718, Japanese Patent Application Laid-Open No. Hei5-320503, and International Patent Publication No. WO95/16737). Highly heat resistant aliphatic polyamides whose main component is a polyamide (PA46) composed of tetramethylenediamine and adipic acid, for example, have also been used. Furthermore, in addition to polyamides, resins with high heat resistance such as liquid crystal polymers (LCP) and polyphenylene sulfide (PPS) have also been used.
However, while the above-mentioned highly heat resistant semi-aromatic polyamides and aliphatic polyamides did have excellent mechanical strength and heat resistance, their flowability and blistering resistance were insufficient in applications where molded articles have been made thinner and lower in profile. The general method to increase flowability is to lower the molecular weight of a resin or a compound thereof. However, since this leads to a decrease in mechanical strength, there is a limit in application of this method to the above-mentioned highly heat resistant semi-aromatic polyamides and aliphatic polyamides.
Also, in the case of an LCP, flowability is excellent, but mechanical strength and sliding properties are poor, and in particular there is a marked decrease in mechanical strength at weld lines where the resins are joined together in an injected molded article, which frequently leads to cracking or wearing during the connector assembly process or in actual use, while in the case of PPS, flowability is low and molding is often difficult.
As described above, the situation is that a material that would satisfy these requirements has not yet to be proposed for SMT connector applications involving reduced thickness and profile height.
Meanwhile, Japanese Patent Application Laid-Open Nos. Sho60-243135 and Hei9-221566, for example, disclose that a fatty acid ester of an alkylene oxide adduct of a bisphenol has excellent heat resistance and is useful as a lubricant for a thermoplastic resin, a releasing agent, a surface lubricity enhancer, or the like. In particular, Japanese Patent Application Laid-Open No. Hei9-221566 lists nylon 6, nylon 66, nylon 11, nylon 12, nylon 46, nylon 610, nylon 612, aromatic polyamide, and other such polyamide resins as examples of thermoplastic resins. Unfortunately, these fatty acid esters did not adequately improve the flowability of polyamide resins.
It is an object of the present invention to provide a polyamide resin composition with excellent flowability as well as excellent blistering resistance, mechanical strength, and sliding properties, and a molded article composed of this composition.
As a result of diligent research to solve the above problems, the present inventors have completed the present invention based on the unexpected discovery that if a specific ester compound is blended with a polyamide resin having a high melting point, the resulting compound will have slightly improved flowability, and that flowability can be markedly improved by further blending with a bromine-based flame retardant.
Specifically, the present invention provides a polyamide resin composition comprising 100 parts by weight of (A) a polyamide resin with a melting point of 270xc2x0 C. to 340xc2x0 C.; 0.2 to 20 parts by weight of (B) a compound represented by Formula (I) 
where R1 and R2 are alkyl groups with a carbon number of at least 9, and m and n are integers from 1 to 3; and
1 to 100 parts by weight of (C) a bromine-based flame retardant.
The present invention also provides a molded article composed of said polyamide resin composition.